A floating bush bearing includes a floating bush rotatably provided in a space between a rotation shaft and a bearing housing. The floating bush bearing is configured so as to supply pressurized lubricating oil from the bearing housing to a space between an inner peripheral surface of the bearing housing and an outer peripheral surface of the floating bush and also to a space between an inner peripheral surface of the floating bush and the rotation shaft via an oil supply path provided in the floating bush in the radial direction.
The floating bush bearing is configured to support the rotation shaft stably while suppressing its oscillation by a damping effect of the oil film of the lubricating oil formed in these spaces and also to prevent seizure.
FIG. 7 is a detailed view of a floating bush bearing for rotatably supporting a rotation shaft of a high-speed rotary machine such as a turbocharger.
In FIG. 7, a turbocharger 0100 is formed by a pair of vane wheels 0102a and 0102b and a rotor shaft 0104 for integrally connecting the pair of vane wheels 0102a and 0102b. A floating bush bearing 0110 is formed by a bearing housing 0112 and a floating bush 0114 placed between the bearing housing 0112 and the rotor shaft 0104. The floating bush 0114 rotatably supports the rotor shaft 0104.
Oil passages 0116 and 0118 are provided in the bearing housing 0112 and the floating bush 0114, respectively. The lubricating oil is supplied from the bearing housing 0112 through the oil passages 0116 and 0118 to the space between the inner peripheral surface of the bearing housing 0112 and the outer peripheral surface of the floating bush 0114 and the space between the inner peripheral surface of the floating bush 0114 and the rotor shaft 0104.
The floating bush 0114 is rotatably arranged and is configured to co-rotate with the rotor shaft 0104 at a speed lower than the rotor shaft 0104 due to sliding resistance against the rotor shaft 0104.
The oil film composed of the lubricating oil is formed in these spaces so as to prevent seizure occurring at a sliding face in the spaces and damage (wear).
In JP 2009-156333 A (Patent Document 1), the width of the inner periphery of the floating bush on the compressor side, Lc is set smaller than the width of the inner periphery of the floating bush on the turbine side, Lt (Lc<Lt). Hence, a spring constant by an oil film on the floating bush bearing on the compressor side is smaller than a sprint constant by an oil film on the floating bush bearing on the turbine side. As a result, without an increase of an eccentricity ratio of the rotor shaft relative to the floating bush bearing on the turbine side subjected to a large bearing load, equilibrium is maintained between the floating bush bearing on the turbine side and the floating bush bearing on the compressor side and natural frequency caused by self-excited oscillation in a high frequency range decreases, thereby achieving noise reduction.
In JP 2007-46642A (Patent Document 2), a spiral groove is provided in at least one of an inner peripheral surface or an outer peripheral surface of a fully floating bearing and that, when the fully floating bearing is rotated, distribution of the pressure loaded on the inner or outer peripheral surface from fluid (lubricating oil) changes along the axial direction by the spiral groove formed in at least one of the inner peripheral surface or the outer peripheral surface. This change makes it difficult for the fully floating bearing to be in a stable state, thereby suppressing self-excited oscillation.